Normal limits of the electrocardiogram in Chinese subjects

International Journal of Cardiology 87 (2003) 37–51 www.elsevier.com / locate / ijcard

Normal limits of the electrocardiogram in Chinese subjects a b, b b a a Jie Wu , Jan A. Kors *, Peter R. Rijnbeek , Gerard van Herpen , Zaiying Lu , Chunfang Xu a

Department of Internal Medicine, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, PR China b Department of Medical Informatics, Faculty of Medicine and Health Sciences, Erasmus University, PO Box 1738, 3000 DR Rotterdam, The Netherlands Received in revised form 30 April 2002; accepted 5 May 2002

Abstract Background: Accurate normal limits of the electrocardiogram (ECG) are the basis on which diagnostic criteria are developed. The ECG, however, is subject to age- and sex-variations and may also be racially determined. Studies into normal ECG limits for the Chinese, comprising one fifth of the world population, are few and have their limitations. We have undertaken to establish normal limits of the ECG from a large sample of healthy Chinese subjects. Methods: Standard simultaneous 12-lead ECGs from 5360 apparently healthy Chinese subjects (3614 men and 1746 women, ages ranging from 18 to 84 years) were collected with a modern digital recorder and processed with a well-validated ECG computer program. The medians, lower limits (2nd percentile) and upper limits (98th percentile) of various ECG measurements were calculated and age and sex differences examined. Results: Significant age trends were present in, for example, P-wave duration, QTc interval, and frontal QRS axis, with concomitant changes of R amplitudes in the extremity leads. Sex differences existed for heart rate, interval durations, the Sokolow and Cornell indices, and QRS and ST-T amplitudes in different leads. Notably, left-precordial R-wave amplitudes in women increased with age; the Sokolow index showed a clearer age trend for men than for women, the reverse being true for the Cornell index. Some of these findings are at odds with established diagnostic ECG criteria. Conclusions: Normal ECG limits of Chinese subjects show marked age and sex differences. This merits the definition and use of age- and sex-specific ECG criteria for a Chinese population.  2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Electrocardiography; Computers; Normal limits; Chinese population

1. Introduction The effect of race on the electrocardiogram (ECG) has been documented in several studies [1–4]. It would thus seem imperative that accurate normal ECG limits be available for the major racial populations, to assist in the development and application of race-specific diagnostic criteria for ECG interpretation. However, there have been remarkably few *Corresponding author. Tel.: 131-10-408-7045; fax: 131-10-4089447. E-mail address: [email protected] (J.A. Kors).

studies into normal ECG limits of the Chinese, comprising one fifth of the total world population. Burns-Cox et al. [5] studied a limited group of 191 young Chinese subjects, men only, and determined ECG measurements by hand. Chen et al. [6] studied a larger cohort of 503 individuals of different ages from Taiwan, both men and women, and used computer-assisted measurement of the ECGs. However, the subgroups that resulted after stratification for age and sex contained only |50 subjects each. Percentile estimates for the upper and lower normal limits derived from such small subgroups are necessarily imprecise.

0167-5273 / 02 / $ – see front matter  2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S0167-5273( 02 )00248-6

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J. Wu et al. / International Journal of Cardiology 87 (2003) 37–51

In this study, we wanted to establish normal limits of the ECG from a large sample of healthy Chinese subjects in whom ECGs were collected with a modern digital recorder and measurements were obtained with a well-validated ECG computer program.

Table 1 Age and sex distribution of the study population Age group (years)

Male

Female

Total

18–29 30–39 40–49 50–59 $60 Total

680 824 819 595 696 3614

424 402 504 255 161 1746

1104 1226 1323 850 857 5360

2. Materials and methods

2.1. Study population All individuals in the study population were taken from regular health examinations of different occupational groups, carried out from 1997 to 1999 in Wuhan, a city of 7 million inhabitants in Central China. A variety of occupations was covered, both sedentary and non-sedentary, e.g. administrators, teachers, engineers, pilots, skilled labourers, policemen, and soldiers. Age ranged from 18 to 84 years. Following recommendations on screening apparently healthy individuals [7], each person who was examined had a medical record including medical history, physical examination, blood pressure, blood biochemistry (glucose, triglycerides, total cholesterol), and chest X-ray. To be included in the study, individuals had to fulfill the following criteria: (i) no history of cardiovascular disease, or any other abnormality known to affect the cardiovascular system; (ii) systolic blood pressure ,140 mmHg and diastolic ,90 mmHg; (iii) no systolic murmur louder than grade 2 / 6, and no diastolic murmur; (iv) plasma triglyceride level #2.3 mmol / l and total cholesterol level #5.2 mmol / l, in accordance with recommendations for assessing lipid metabolic disorder [8,9]; (5) plasma glucose level #5.6 mmol / l; (6) no abnormal heart or lung findings on chest X-ray. A total of 5448 individuals met the above inclusion criteria. Of these, 74 were found to have a right bundle branch block (RBBB) and four a left bundle branch block (LBBB), according to established ECG criteria [10]. They were excluded from the study population. In addition, ten cases that presented with a clear Wolff-Parkinson-White pattern were also excluded. Thus, the final study population consisted of 5360 individuals. The study population was divided into five age

groups: 18–29, 30–39, 40–49, 50–59 years, and 60 years and older. Table 1 shows the number of men and women in each of the age groups.

2.2. ECG measurements Standard simultaneous 12-lead ECGs were recorded at a sampling rate of 1200 Hz with the use of a PC-based acquisition system (Cardio Control, Delft, The Netherlands), and stored for subsequent processing. All recordings were made by the same technician. The ECGs were processed by the Modular ECG Analysis System (MEANS) [11]. The performance of MEANS has been extensively evaluated both by the developers themselves [11] and by others [12,13]. For each of the 12 leads, MEANS computes a representative averaged beat from which ECG measurements are derived. All ECGs were visually checked for correct identification by the computer of onset and offset of the P wave and the QRS complex as well as of the end of the T wave. In 77 cases (1.4%), the P-wave fiducial points determined by MEANS were considered incorrect. These cases were excluded from subsequent analyses involving P-wave measurements. An erroneous end of the T wave was detected in one case, which was excluded from further T-wave measurement; no waveform recognition errors were found for the QRS complex. Measurements of wave amplitudes and durations were made in accordance with previous recommendations [14]. P-wave amplitude was measured with respect to the baseline before P onset. The baseline before QRS onset was used to measure all amplitudes in the QRS-T complex. Q-wave duration was measured from its onset within an individual lead. P and QRS duration and QT interval were determined from common P and QRS onsets and offsets and T offset for all 12 leads together. A corrected QT (QTc) interval was computed with the use of Bazett’s

J. Wu et al. / International Journal of Cardiology 87 (2003) 37–51

formula [15]. Following previous recommendations [10], R peak time (intrinsicoid deflection) in a lead was measured from overall QRS onset to the peak of the R wave or, if present, the R9 wave in that lead. QRS and T axis determinations were based on wave areas [10]. For comparison purposes, axes were also computed from lead amplitudes.

2.3. Statistical analysis The 2nd and 98th percentiles of the measurement distributions were taken as the lower and upper limits, respectively, of normal. Also, medians of the parameters were calculated. Zero amplitude values, indicating absent Q, R, or S waves, were excluded from the analyses. Differences in parameter distributions between men and women were compared with the Mann–Whitney test [16]. Age trends across the age groups were tested with Cuzick’s test [16,17]. P-values ,0.05 were considered as significant. All statistical analyses were performed with the Intercooled Stata 7.0 software package (Stata Corporation, College Station, USA).

39

3. Results

3.1. Global measurements All participants were in sinus rhythm. Table 2 shows normal limits of heart rate, overall durations and intervals, and frontal-plane axes. Apart from QRS duration in women, all global parameters showed significant age trends; sex differences were observed for all parameters except QRS axis. Median values and most limits for QRS and T axes proved very comparable for the two axis computation methods, the lower limit for QRS axis however tending to be lower when the area method was used. The upper limit of normal sinus heart rate is |95 beats / min for men and women. The lower limit in men is 51 beats / min. In women, the lower limit decreases from 57 to 51 beats / min with increasing age. Upper limits for P-wave duration range from 125 to 141 ms, with a small but consistent difference between men and women, and increase with age. Median PR intervals increase with age, with men having a 10 ms longer PR interval than women. The

Table 2 Global ECG parameters: median (2nd percentile, 98th percentile) Sex

18–29 Years

30–39 Years

40–49 Years

50–59 Years

$60 Years

Trend

Heart rate (bpm)

Male Female

67 (51, 96) 73 (57, 101)***

68 (52, 94) 71 (56, 94)***

67 (51, 93) 68 (55, 91)**

67 (53, 92) 67 (51, 95)

68 (51, 97) 68 (51, 99)

** ***

P duration (ms)

Male Female

111 (92, 133) 105 (86, 125)***

113 (93, 134) 107 (91, 128)***

114 (93, 135) 110 (90, 128)***

116 (94, 138) 113 (90, 133)***

118 (94, 141) 113 (91, 136)***

*** ***

PR interval (ms)

Male Female

149 (117, 198) 139 (109, 182)***

153 (121, 198) 143 (117, 183)***

155 (122, 198) 146 (116, 185)***

158 (127, 202) 149 (124, 193)***

159 (125, 206) 152 (115, 199)***

*** ***

QRS axis (8) (areas)

Male Female

70 (254, 109) 70 (231, 101)

64 (250, 100) 66 (227, 96)

53 (271, 92) 51 (224, 91)

45 (258, 89) 47 (237, 85)

43 (274, 95) 44 (250, 88)

*** ***

QRS axis (8) (amplitudes)

Male Female

71 (215, 104) 72 (216, 98)

64 (234, 96) 67 (24, 96)**

52 (244, 91) 53 (219, 89)

43 (238, 87) 47 (244, 83)

42 (255, 93) 42 (252, 87)

*** ***

QRS duration (ms)

Male Female

94 (73, 119) 87 (66, 108)***

96 (74, 120) 90 (69, 109)***

95 (74, 121) 89 (68, 109)***

94 (73, 118) 87 (67, 107)***

93 (73, 120) 86 (64, 109)***

***

QT interval (ms)

Male Female

374 (329, 417) 378 (326, 430)

377 (333, 425) 388 (340, 446)***

383 (338, 432) 397 (348, 451)***

387 (340, 437) 403 (351, 462)***

388 (339, 441) 399 (349, 467)***

*** ***

QTc interval (ms)

Male Female

396 (355, 443) 418 (378, 459)***

400 (363, 442) 420 (383, 458)***

404 (368, 449) 424 (388, 469)***

411 (369, 456) 426 (385, 472)***

416 (378, 468) 427 (388, 487)***

*** ***

T axis (8) (areas)

Male Female

51 (5, 77) 44 (214, 70)***

46 (2, 76) 41 (25, 71)***

44 (25, 74) 37 (213, 67)***

42 (215, 77) 36 (221, 85)***

49 (216, 83) 43 (244, 96)***

** **

T axis (8) (amplitudes)

Male Female

50 (7, 77) 45 (0, 68)***

47 (0, 75) 43 (0, 72)***

44 (0, 73) 38 (210, 66)***

42 (211, 75) 37 (217, 74)***

50 (29, 82) 43 (210, 78)***

* ***

*P,0.05, **P,0.01, ***P,0.001, Mann–Whitney test for sex differences, Cuzick’s test for age trend.

J. Wu et al. / International Journal of Cardiology 87 (2003) 37–51

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upper limit of the PR interval is |200 ms in men; in women, the upper limit gradually increases with age from 180 to 200 ms. The upper limit of QRS duration was |120 ms for men and 109 ms for women. Upper limits of the QTc interval tended to increase with age in both sexes, and were always .440 ms, the clinically accepted normal limit. Also, for all age groups upper limits in women were 16–20 ms higher than in men. Median QRS axis gradually shifted to the left by |258 over the total age range, both in men and women. T axis proved relatively stable.

3.2. P-wave amplitude Table 3 shows the normal limits of the P-wave amplitude. Since P waves in lead aVR are mainly

negative and the negative component of the P wave in V1 is of clinical interest, negative amplitude values are listed for these two leads. P-wave amplitude is hardly affected by age and sex. The upper limit of P-wave amplitude was ,0.20 mV in the limb leads and ,0.10 mV in the precordial leads. In lead V1 , the negative deflection was 0.11 mV or less.

3.3. Q-wave amplitude and duration Normal limits of Q-wave duration, Q-wave amplitude, and the prevalence of QS patterns are presented in Tables 4–6, respectively. In previous studies [6,18], QS waves were included in the derivation of normal limits for Q waves. However, the distinction between Q and QS waves is important from a clinical point of view; they also have been defined differently [14]. We therefore chose to treat Q

Table 3 P-wave amplitude (mV): median (98th percentile) Lead

Sex

18–29 Years

30–39 Years

40–49 Years

50–59 Years

$60 Years

I

Male Female

0.05 (0.09) 0.06 (0.10)

0.05 (0.10) 0.05 (0.09)

0.06 (0.10) 0.06 (0.10)

0.06 (0.10) 0.06 (0.10)

0.06 (0.10) 0.07 (0.11)

II

Male Female

0.10 (0.19) 0.09 (0.20)

0.09 (0.19) 0.10 (0.18)

0.09 (0.17) 0.09 (0.15)

0.10 (0.17) 0.09 (0.16)

0.10 (0.19) 0.09 (0.18)

III

Male Female

0.07 (0.15) 0.06 (0.16)

0.06 (0.16) 0.07 (0.14)

0.06 (0.14) 0.06 (0.13)

0.07 (0.15) 0.06 (0.13)

0.07 (0.16) 0.06 (0.15)

aVR (P2)

Male Female

0.07 (0.11) 0.07 (0.12)

0.07 (0.12) 0.07 (0.11)

0.07 (0.11) 0.07 (0.11)

0.07 (0.11) 0.07 (0.12)

0.07 (0.12) 0.07 (0.12)

aVL

Male Female

0.04 (0.08) 0.04 (0.08)

0.04 (0.07) 0.04 (0.08)

0.04 (0.07) 0.04 (0.08)

0.04 (0.08) 0.04 (0.08)

0.04 (0.08) 0.04 (0.08)

aVF

Male Female

0.08 (0.16) 0.07 (0.17)

0.07 (0.17) 0.08 (0.15)

0.07 (0.15) 0.07 (0.13)

0.08 (0.16) 0.07 (0.14)

0.08 (0.17) 0.07 (0.17)

V1 (P1)

Male Female

0.05 (0.09) 0.04 (0.09)

0.05 (0.09) 0.04 (0.08)

0.04 (0.08) 0.04 (0.08)

0.04 (0.08) 0.04 (0.08)

0.04 (0.07) 0.04 (0.08)

V1 (P2)

Male Female

0.04 (0.09) 0.04 (0.07)

0.04 (0.08) 0.03 (0.06)

0.04 (0.08) 0.04 (0.07)

0.05 (0.10) 0.04 (0.07)

0.05 (0.11) 0.04 (0.08)

V2

Male Female

0.05 (0.10) 0.05 (0.09)

0.05 (0.09) 0.05 (0.09)

0.05 (0.10) 0.05 (0.09)

0.05 (0.10) 0.05 (0.09)

0.05 (0.09) 0.05 (0.10)

V3

Male Female

0.05 (0.10) 0.05 (0.09)

0.05 (0.09) 0.05 (0.09)

0.05 (0.10) 0.05 (0.09)

0.05 (0.10) 0.06 (0.09)

0.05 (0.10) 0.05 (0.10)

V4

Male Female

0.05 (0.09) 0.05 (0.09)

0.05 (0.09) 0.05 (0.08)

0.06 (0.09) 0.05 (0.09)

0.06 (0.10) 0.06 (0.09)

0.06 (0.10) 0.06 (0.10)

V5

Male Female

0.05 (0.09) 0.05 (0.08)

0.05 (0.08) 0.05 (0.09)

0.05 (0.08) 0.05 (0.08)

0.06 (0.09) 0.05 (0.09)

0.06 (0.09) 0.06 (0.10)

V6

Male Female

0.05 (0.08) 0.05 (0.08)

0.05 (0.08) 0.05 (0.08)

0.05 (0.08) 0.05 (0.08)

0.06 (0.08) 0.05 (0.08)

0.06 (0.09) 0.06 (0.10)

J. Wu et al. / International Journal of Cardiology 87 (2003) 37–51

41

Table 4 Q-wave duration (ms): median (98th percentile) Lead

Sex

18–29 Years

30–39 Years

40–49 Years

50–59 Years

$60 Years

I

Male

17 (26) n5131 16 (25) n551

16 (24) n5155 16 (22) n551

17 (28) n5162 15 (22) n597

17 (25) n5129 15 (23) n552

15 (25) n5156 14 (21) n530

20 (28) n5194 18 (24) n5100

19 (28) n5192 18 (26) n578

19 (28) n5150 19 (28) n5105

20 (30) n595 19 (26) n538

19 (29) n5130 20 (29) n524

19 (30) n5313 18 (27) n5191

19 (37) n5339 18 (28) n5148

20 (40) n5281 18 (34) n5173

22 (44) n5237 20 (40) n585

20 (43) n5209 22 (41) n553

40 (52) n5357 39 (47) n5208

39 (50) n5411 39 (48) n5193

40 (52) n5382 39 (50) n5191

39 (49) n5258 38 (49) n5104

39 (51) n5342 38 (48) n566

23 (54) n5196 25 (46) n5107

22 (49) n5251 24 (46) n5114

20 (45) n5269 19 (47) n5143

19 (47) n5197 17 (37) n573

20 (39) n5268 17 (38) n548

18 (25) n5232 16 (23) n5140

18 (26) n5244 16 (24) n5106

17 (28) n5182 18 (29) n5107

18 (28) n5150 17 (27) n545

18 (29) n5158 19 (33) n538

–

–

n51

–

37 (40) n55 –

–

n51 –

– –

Female II

Male Female

III

Male Female

aVR

Male Female

aVL

Male Female

aVF

Male Female

V1

Male

–

Female

–

n51 –

V2

Male Female

– –

– –

V3

Male

13 (17) n56 15 (17) n53

n52 –

15 (25) n598 12 (22) n528

Female V4

Male Female

V5

Male Female

V6

Male Female

n51 n52 14 (18) n54

n52 10 (17) n54

n51

13 (24) n578 11 (22) n519

14 (24) n559 14 (21) n550

14 (22) n545 12 (22) n519

13 (30) n571 13 (17) n59

16 (25) n5245 14 (23) n569

15 (24) n5247 13 (22) n555

14 (24) n5204 15 (22) n5113

14 (22) n5124 14 (23) n549

15 (24) n5165 14 (19) n525

18 (28) n5299 16 (23) n5123

17 (25) n5314 15 (23) n598

16 (25) n5259 16 (22) n5159

16 (25) n5174 14 (23) n571

16 (23) n5200 14 (22) n535

waves and QS patterns separately. The upper limit of Q-wave duration in women was generally a little shorter than in men (Table 4). Except for lead III, there was hardly any age-effect. Q waves were

11 (48) n58

extremely rare in leads V1 and V2 . Only 1.6% (n583) of the subjects had a QS pattern in V1 ; QS patterns seldom occur in V2 (n59) and aVF (n516). Table 7 shows normal limits of the Q / R amplitude

J. Wu et al. / International Journal of Cardiology 87 (2003) 37–51

42

Table 5 Q-wave amplitude (mV): median (98th percentile) Lead

Sex

18–29 Years

30–39 Years

40–49 Years

50–59 Years

$60 Years

I

Male Female

0.05 (0.16) 0.05 (0.13)

0.05 (0.16) 0.05 (0.13)

0.05 (0.13) 0.05 (0.13)

0.05 (0.17) 0.05 (0.12)

0.05 (0.14) 0.05 (0.12)

II

Male Female

0.06 (0.26) 0.05 (0.22)

0.06 (0.14) 0.05 (0.21)

0.05 (0.16) 0.05 (0.15)

0.05 (0.23) 0.05 (0.12)

0.06 (0.19) 0.06 (0.14)

III

Male Female

0.10 (0.40) 0.07 (0.27)

0.08 (0.48) 0.07 (0.29)

0.10 (0.50) 0.08 (0.30)

0.12 (0.62) 0.11 (0.54)

0.09 (0.48) 0.13 (0.62)

aVR

Male Female

0.73 (1.26) 0.62 (1.00)

0.66 (1.11) 0.57 (0.96)

0.67 (1.10) 0.61 (1.04)

0.60 (1.05) 0.58 (1.09)

0.55 (1.02) 0.61 (1.30)

aVL

Male Female

0.10 (0.58) 0.13 (0.50)

0.09 (0.39) 0.10 (0.48)

0.08 (0.46) 0.07 (0.39)

0.07 (0.36) 0.06 (0.26)

0.07 (0.31) 0.07 (0.30)

aVF

Male Female

0.07 (0.28) 0.06 (0.22)

0.06 (0.17) 0.06 (0.20)

0.06 (0.22) 0.06 (0.19)

0.07 (0.26) 0.07 (0.25)

0.06 (0.25) 0.07 (0.24)

V1

Male Female

– –

– –

– –

– –

0.15 (0.58) –

V2

Male Female

– –

– –

– –

– –

– –

V3

Male Female

0.05 (0.11) 0.05 (0.13)

– –

– 0.07 (0.15)

– 0.05 (0.09)

0.05 (0.78) –

V4

Male Female

0.06 (0.37) 0.05 (0.22)

0.05 (0.40) 0.04 (0.15)

0.05 (0.24) 0.06 (0.15)

0.05 (0.20) 0.06 (0.19)

0.06 (0.50) 0.04 (0.13)

V5

Male Female

0.07 (0.37) 0.05 (0.21)

0.06 (0.29) 0.05 (0.23)

0.05 (0.23) 0.05 (0.17)

0.05 (0.24) 0.06 (0.19)

0.06 (0.28) 0.05 (0.14)

V6

Male Female

0.07 (0.30) 0.06 (0.21)

0.06 (0.23) 0.05 (0.18)

0.05 (0.16) 0.06 (0.16)

0.05 (0.16) 0.05 (0.20)

0.06 (0.21) 0.05 (0.13)

ratio for selected leads. Q / R ratio was ,25% for leads I and II, and ,15% for leads V5 and V6 , except for the young. In lead aVF, the Q / R ratio in some age groups was larger because of cases with very small Q and R wave amplitudes that yielded a large ratio.

3.4. R- and S-wave amplitudes The normal limits for R- and S-wave amplitudes, as well as R / S amplitude ratio are shown in Tables 8–10, respectively. Table 8 also lists the normal limits of the Sokolow-Lyon index (SV1 1RV5 ) and the Cornell voltage index (RaVL1SV3 ) for the Table 6 Number (%) of QS patterns in leads III, aVR, aVL, and V1

Male Female

III

aVR

aVL

V1

40 (1.1) 14 (0.8)

1040 (28.8) 629 (36.0)

199 (5.5) 93 (5.3)

51 (1.4) 32 (1.8)

different age groups. Most amplitudes showed a significant age trend. Differences between men and women were largest in the younger age groups, but tended to diminish with increasing age. In the limb leads, the median R-wave amplitude in lead aVL showed a twofold increase with age in men (from 0.16 to 0.32 mV) and a threefold increase in women (0.11 to 0.32 mV). R amplitude in lead I also tended to increase with age, more prominently in women than in men. Conversely, R amplitude in the inferior leads II, III and aVF consistently decreased with increasing age in both sexes. In lead aVF, for instance, the median R-wave amplitude decreased by 0.47 mV in men and by 0.37 mV in women, while the upper normal limit decreased by |0.65 mV in both sexes. Notably, the upper limits of R amplitude in leads II, III and aVF in the 18–29 age group were substantially higher than in the other age groups. With increasing age, sex differences in median Rwave amplitude tended to disappear, whereas the

J. Wu et al. / International Journal of Cardiology 87 (2003) 37–51

43

Table 7 Q / R ratio: median (98th percentile) Lead

Sex

18–29 Years

30–39 Years

40–49 Years

50–59 Years

$60 Years

I

Male Female

0.07 (0.21) 0.08 (0.24)

0.07 (0.23) 0.08 (0.25)

0.07 (0.18) 0.07 (0.18)

0.06 (0.17) 0.06 (0.15)

0.07 (0.22) 0.06 (0.12)

II

Male Female

0.04 (0.12) 0.04 (0.12)

0.04 (0.11) 0.04 (0.12)

0.04 (0.13) 0.05 (0.15)

0.04 (0.21) 0.04 (0.10)

0.05 (0.31) 0.07 (0.21)

III

Male Female

0.09 (0.82) 0.08 (0.44)

0.10 (1.54) 0.09 (0.82)

0.14 (2.69) 0.12 (2.02)

0.23 (3.89) 0.21 (3.57)

0.13 (3.53) 0.21 (3.76)

aVF

Male Female

0.05 (0.21) 0.05 (0.15)

0.06 (0.60) 0.05 (0.17)

0.07 (1.43) 0.07 (0.31)

0.08 (1.25) 0.08 (0.80)

0.08 (1.26) 0.11 (3.42)

V5

Male Female

0.03 (0.16) 0.03 (0.11)

0.03 (0.12) 0.03 (0.13)

0.03 (0.09) 0.04 (0.09)

0.03 (0.12) 0.03 (0.10)

0.03 (0.12) 0.03 (0.07)

V6

Male Female

0.04 (0.18) 0.04 (0.12)

0.04 (0.14) 0.04 (0.13)

0.04 (0.11) 0.04 (0.11)

0.04 (0.11) 0.04 (0.12)

0.04 (0.12) 0.03 (0.10)

Table 8 R-wave amplitude and Sokolow and Cornell indices (mV): median (2nd percentile, 98th percentile) Lead

Sex

18–29 Years

30–39 Years

40–49 Years

50–59 Years

$60 Years

Trend

I

Male Female

0.45 (0.11, 1.10) 0.35 (0.10, 0.96)***

0.50 (0.12, 1.20) 0.36 (0.11, 0.90)***

0.58 (0.14, 1.18) 0.53 (0.14, 1.11)**

0.61 (0.15, 1.21) 0.59 (0.18, 1.28)

0.56 (0.12, 1.17) 0.60 (0.18, 1.43)*

*** ***

II

Male Female

1.21 (0.43, 2.20) 1.07 (0.46, 1.98)***

1.02 (0.38, 1.87) 0.98 (0.38, 1.71)**

0.90 (0.29, 1.80) 0.90 (0.33, 1.64)

0.78 (0.21, 1.69) 0.80 (0.27, 1.55)

0.73 (0.13, 1.57) 0.78 (0.10, 1.41)

*** ***

III

Male Female

0.81 (0.06, 2.02) 0.76 (0.13, 1.66)

0.62 (0.05, 1.53) 0.60 (0.07, 1.39)

0.43 (0.04, 1.45) 0.42 (0.04, 1.33)

0.31 (0.04, 1.33) 0.36 (0.04, 1.12)

0.35 (0.04, 1.29) 0.34 (0.03, 0.96)

*** ***

aVR

Male Female

0.14 (0.04, 0.43) 0.12 (0.03, 0.38)**

0.14 (0.03, 0.40) 0.11 (0.03, 0.33)***

0.13 (0.03, 0.41) 0.08 (0.03, 0.31)***

0.12 (0.03, 0.39) 0.09 (0.03, 0.34)***

0.13 (0.03, 0.41) 0.12 (0.03, 0.34)

** **

aVL

Male Female

0.16 (0.04, 0.67) 0.11 (0.04, 0.57)***

0.21 (0.04, 0.90) 0.13 (0.04, 0.53)***

0.27 (0.04, 0.89) 0.20 (0.04, 0.80)***

0.33 (0.05, 0.98) 0.30 (0.05, 0.94)

0.32 (0.04, 0.97) 0.32 (0.04, 1.23)

*** ***

aVF

Male Female

0.99 (0.24, 2.05) 0.90 (0.28, 1.77)

0.80 (0.13, 1.68) 0.78 (0.23, 1.46)

0.64 (0.08, 1.61) 0.65 (0.13, 1.41)

0.51 (0.05, 1.49) 0.56 (0.06, 1.29)

0.52 (0.05, 1.37) 0.53 (0.04, 1.14)

*** ***

V1

Male Female

0.43 (0.07, 1.21) 0.30 (0.05, 1.00)***

0.34 (0.07, 0.93) 0.24 (0.04, 0.80)***

0.28 (0.06, 0.96) 0.23 (0.05, 0.72)***

0.26 (0.05, 0.77) 0.23 (0.04, 0.72)

0.22 (0.05, 0.80) 0.21 (0.04, 0.87)

*** ***

V2

Male Female

0.91 (0.24, 2.06) 0.66 (0.12, 1.50)***

0.78 (0.17, 1.65) 0.53 (0.12, 1.34)***

0.72 (0.17, 1.67) 0.58 (0.10, 1.26)***

0.71 (0.14, 1.74) 0.61 (0.14, 1.60)***

0.66 (0.11, 1.70) 0.66 (0.09, 1.53)

***

V3

Male Female

1.12 (0.40, 2.59) 0.91 (0.26, 2.06)***

1.07 (0.35, 2.29) 0.85 (0.21, 1.93)***

1.08 (0.30, 2.28) 0.93 (0.25, 1.91)***

1.16 (0.28, 2.29) 1.04 (0.37, 2.11)**

1.12 (0.24, 2.51) 1.17 (0.32, 2.23)

***

V4

Male Female

1.95 (0.85, 3.16) 1.25 (0.47, 2.21)***

1.80 (0.80, 2.93) 1.28 (0.54, 2.17)***

1.75 (0.87, 2.86) 1.34 (0.64, 2.51)***

1.80 (0.74, 2.82) 1.48 (0.74, 2.60)***

1.76 (0.70, 2.81) 1.59 (0.77, 2.73)***

*** ***

V5

Male Female

1.71 (0.87, 2.88) 1.17 (0.59, 1.99)***

1.59 (0.80, 2.80) 1.16 (0.56, 2.02)***

1.55 (0.77, 2.55) 1.24 (0.59, 2.13)***

1.59 (0.79, 2.56) 1.37 (0.73, 2.38)***

1.59 (0.77, 2.73) 1.42 (0.69, 2.57)***

*** ***

V6

Male Female

1.32 (0.68, 2.14) 1.01 (0.55, 1.73)***

1.21 (0.59, 2.10) 0.98 (0.47, 1.63)***

1.15 (0.56, 1.96) 1.01 (0.48, 1.74)***

1.16 (0.53, 2.03) 1.08 (0.57, 1.94)***

1.16 (0.47, 2.15) 1.12 (0.47, 2.08)

*** ***

Sokolow index (SV1 1RV5 )

Male Female

2.89 (1.58, 4.49) 2.09 (1.20, 3.63)***

2.60 (1.45, 4.23) 2.11 (1.05, 3.33)***

2.50 (1.37, 4.11) 2.07 (1.11, 3.51)***

2.48 (1.36, 4.02) 2.15 (1.20, 3.60)***

2.39 (1.25, 4.05) 2.16 (1.20, 3.58)***

***

Cornell index (RaVL1SV3 )

Male Female

1.28 (0.12, 2.74) 0.77 (0.10, 1.66)***

1.29 (0.29, 2.59) 0.78 (0.13, 1.72)***

1.31 (0.35, 2.62) 0.80 (0.16, 1.70)***

1.39 (0.40, 2.67) 1.05 (0.29, 2.02)***

1.40 (0.47, 2.75) 1.24 (0.34, 2.58)***

*** ***

*P,0.05, **P,0.01, ***P,0.001; Mann–Whitney test for sex differences, Cuzick’s test for age trend.

J. Wu et al. / International Journal of Cardiology 87 (2003) 37–51

44

Table 9 S-wave amplitude (mV): median (2nd percentile, 98th percentile) Lead

Sex

18–29 Years

30–39 Years

40–49 Years

50–59 Years

$60 Years

Trend

I

Male Female

0.17 (0.06, 0.55) 0.13 (0.06, 0.41)***

0.18 (0.05, 0.50) 0.13 (0.05, 0.37)***

0.15 (0.05, 0.49) 0.11 (0.05, 0.34)***

0.14 (0.05, 0.41) 0.11 (0.05, 0.38)**

0.14 (0.06, 0.42) 0.14 (0.05, 0.50)

***

II

Male Female

0.22 (0.07, 0.63) 0.17 (0.05, 0.54)***

0.20 (0.06, 0.61) 0.17 (0.06, 0.48)***

0.19 (0.06, 0.67) 0.16 (0.06, 0.51)***

0.18 (0.06, 0.61) 0.16 (0.05, 0.54)

0.22 (0.05, 0.64) 0.19 (0.05, 0.59)

III

Male Female

0.21 (0.06, 0.84) 0.18 (0.06, 0.67)*

0.22 (0.06, 0.84) 0.19 (0.06, 0.56)**

0.23 (0.06, 0.96) 0.18 (0.06, 0.68)***

0.27 (0.05, 1.00) 0.22 (0.05, 0.87)*

0.30 (0.06, 1.09) 0.27 (0.05, 1.27)

*** ***

aVR

Male Female

1.05 (0.67, 1.50) 0.87 (0.56, 1.55)***

0.93 (0.51, 1.44) 0.81 (0.44, 1.28)***

0.86 (0.51, 1.44) 0.86 (0.47, 1.19)

0.83 (0.44, 1.47) 0.86 (0.46, 1.43)

0.79 (0.42, 1.21) 0.70 (0.52, 1.05)

*** *

aVL

Male Female

0.37 (0.06, 1.03) 0.35 (0.06, 0.88)

0.29 (0.06, 0.78) 0.25 (0.05, 0.74)*

0.24 (0.05, 0.77) 0.20 (0.05, 0.65)*

0.21 (0.06, 0.65) 0.20 (0.05, 0.59)

0.20 (0.05, 0.68) 0.20 (0.04, 0.72)

*** ***

aVF

Male Female

0.20 (0.06, 0.71) 0.17 (0.05, 0.53)*

0.19 (0.06, 0.62) 0.17 (0.05, 0.49)

0.19 (0.06, 0.77) 0.15 (0.05, 0.50)*

0.16 (0.05, 0.68) 0.16 (0.05, 0.57)*

0.22 (0.06, 0.82) 0.19 (0.06, 0.93)

V1

Male Female

1.12 (0.31, 2.43) 0.87 (0.36, 2.02)***

1.01 (0.30, 2.08) 0.88 (0.25, 2.03)***

0.93 (0.26, 1.95) 0.81 (0.27, 1.69)***

0.86 (0.22, 2.02) 0.73 (0.16, 1.62)***

0.78 (0.21, 1.77) 0.70 (0.21, 1.59)**

*** ***

V2

Male Female

1.82 (0.45, 3.34) 1.13 (0.28, 2.29)***

1.58 (0.45, 2.95) 1.11 (0.30, 2.28)***

1.46 (0.51, 2.82) 0.97 (0.28, 2.14)***

1.35 (0.50, 2.54) 1.02 (0.25, 2.05)***

1.19 (0.38, 2.36) 1.09 (0.31, 2.09)**

*** ***

V3

Male Female

1.11 (0.30, 2.52) 0.65 (0.19, 1.40)***

1.04 (0.25, 2.28) 0.64 (0.19, 1.60)***

1.01 (0.29, 2.23) 0.58 (0.14, 1.39)***

1.05 (0.31, 2.21) 0.74 (0.17, 1.65)***

1.09 (0.26, 2.09) 0.88 (0.20, 1.97)***

***

V4

Male Female

0.67 (0.15, 1.71) 0.42 (0.15, 0.99)***

0.63 (0.17, 1.53) 0.41 (0.11, 0.89)***

0.63 (0.17, 1.54) 0.36 (0.10, 0.93)***

0.67 (0.17, 1.66) 0.47 (0.15, 1.09)***

0.74 (0.21, 1.71) 0.56 (0.17, 1.47)***

*** ***

V5

Male Female

0.35 (0.09, 0.95) 0.25 (0.07, 0.76)***

0.31 (0.08, 0.96) 0.24 (0.06, 0.58)***

0.31 (0.08, 0.96) 0.21 (0.06, 0.69)***

0.34 (0.07, 1.01) 0.24 (0.05, 0.71)***

0.39 (0.07, 1.04) 0.32 (0.07, 1.07)**

***

V6

Male Female

0.19 (0.07, 0.55) 0.16 (0.05, 0.45)***

0.19 (0.06, 0.54) 0.14 (0.06, 0.39)***

0.17 (0.06, 0.61) 0.13 (0.05, 0.42)***

0.19 (0.06, 0.59) 0.15 (0.05, 0.50)***

0.22 (0.06, 0.64) 0.17 (0.06, 0.70)**

*P,0.05, **P,0.01, ***P,0.001; Mann–Whitney test for sex differences, Cuzick’s test for age trend.

upper limits showed a consistent sex difference over all age groups. The R-amplitude trend in V5 was more complex. In men, the median amplitude was relatively stable with age, except in young subjects who had slightly higher voltages. The upper normal limit tended to decrease with age, while increasing again over the age of 60. Interestingly, in women both median and upper limit of the R amplitude in lead V5 increased with age, contrary to the generally accepted view that R-wave amplitudes tend to decrease with age. As to the Sokolow index, men showed a significant age trend whereas women did not. In men, the median Sokolow index decreased considerably with age (2.89–2.39 mV), as did the upper normal limit (4.49–4.05 mV); in women, the index fluctuated only slightly. The median Cornell index increased with age both for men and women, but the upper normal limit in men did not change much. Both indices showed highly significant sex differences for all age

groups, but differences became smaller with increasing age.

3.5. ST-T amplitudes Normal limits of the J-point amplitude are given in Table 11. In the limb leads, sex differences in the median J-point amplitude were small. Prominent sex differences were mainly present in leads V2 –V4 in the young, but markedly diminished in older subjects. Generally, women had deeper negative J-point voltages. The lower normal limit of J-point depression ranges from 0.04 to 0.08 mV in leads I, II, and aVF, and from 0.06 to 0.12 mV in the left precordial leads V5 and V6 . Tables 12 and 13 show the normal limits of the positive and negative T-wave amplitude in each lead. Inverted T waves were rare in leads I and II, as might be expected. In our data, the prevalence was 0.5% in lead I and 1.6% in lead II. An inverted or diphasic T

J. Wu et al. / International Journal of Cardiology 87 (2003) 37–51

45

Table 10 R / S ratio: median (2nd percentile, 98th percentile) Lead

Sex

18–29 Years

30–39 Years

40–49 Years

50–59 Years

$60 Years

I

Male Female

2.41 (0.40, 11.05) 2.21 (0.40, 9.87)

2.71 (0.54, 11.56) 2.56 (0.49, 10.89)

3.49 (0.66, 13.85) 4.25 (0.76, 14.54)

3.82 (0.79, 15.66) 4.41 (0.74, 21.86)

3.58 (0.55, 15.88) 5.01 (1.01, 20.01)

II

Male Female

5.00 (1.02, 20.46) 6.15 (1.04, 25.98)

4.43 (0.80, 22.13) 4.97 (1.17, 19.50)

4.06 (0.44, 19.39) 5.55 (1.02, 19.41)

3.64 (0.51, 15.49) 4.36 (0.47, 21.85)

2.90 (0.28, 14.75) 3.93 (0.25, 15.45)

III

Male Female

3.04 (0.22, 19.58) 3.91 (0.20, 18.82)

2.10 (0.10, 16.27) 2.91 (0.19, 14.68)

1.37 (0.11, 13.04) 1.59 (0.10, 13.24)

0.72 (0.10, 10.33) 1.22 (0.07, 12.04)

0.70 (0.08, 10.41) 1.09 (0.05, 12.51)

aVR

Male Female

0.05 (0.02, 0.15) 0.05 (0.02, 0.12)

0.05 (0.02, 0.12) 0.05 (0.03, 0.11)

0.05 (0.02, 0.12) 0.05 (0.03, 0.13)

0.05 (0.03, 0.20) 0.05 (0.02, 0.11)

0.06 (0.03, 0.15) 0.06 (0.03, 0.12)

aVL

Male Female

0.37 (0.07, 6.12) 0.25 (0.09, 6.04)

0.64 (0.08, 6.87) 0.39 (0.09, 3.04)

1.08 (0.08, 8.24) 0.74 (0.12, 7.75)

1.55 (0.09, 8.98) 1.32 (0.13, 8.14)

1.36 (0.09, 11.59) 1.54 (0.12, 7.14)

aVF

Male Female

4.27 (0.61, 20.15) 5.27 (0.59, 26.83)

3.34 (0.30, 17.84) 3.89 (0.72, 18.56)

2.73 (0.16, 16.00) 3.93 (0.29, 18.65)

2.01 (0.19, 14.16) 2.87 (0.19, 20.27)

1.54 (0.12, 12.68) 2.53 (0.04, 12.30)

V1

Male Female

0.38 (0.05, 1.44) 0.35 (0.05, 1.19)

0.35 (0.06, 1.19) 0.26 (0.04, 1.09)

0.30 (0.04, 1.34) 0.29 (0.05, 1.13)

0.28 (0.04, 1.40) 0.31 (0.05, 1.63)

0.27 (0.04, 1.55) 0.33 (0.06, 1.78)

V2

Male Female

0.50 (0.12, 2.06) 0.56 (0.09, 3.05)

0.54 (0.08, 1.91) 0.48 (0.07, 2.40)

0.51 (0.08, 1.83) 0.62 (0.07, 2.96)

0.54 (0.08, 1.90) 0.61 (0.15, 2.67)

0.54 (0.08, 2.29) 0.63 (0.09, 1.86)

V3

Male Female

0.98 (0.26, 5.97) 1.30 (0.38, 6.96)

0.97 (0.25, 5.47) 1.38 (0.32, 5.62)

1.05 (0.23, 4.99) 1.57 (0.37, 8.44)

1.13 (0.20, 5.12) 1.42 (0.39, 7.44)

1.06 (0.14, 4.66) 1.31 (0.32, 4.73)

V4

Male Female

2.90 (0.70, 15.76) 2.95 (0.72, 10.94)

2.80 (0.80, 13.25) 3.16 (0.80, 15.30)

2.79 (0.82, 11.91) 3.60 (0.97, 18.04)

2.63 (0.74, 12.12) 3.32 (1.07, 12.63)

2.33 (0.62, 11.54) 2.80 (0.72, 11.85)

V5

Male Female

4.86 (1.17, 19.42) 4.58 (0.99, 17.82)

5.09 (1.29, 25.07) 4.76 (1.34, 20.24)

5.06 (1.24, 18.19) 5.86 (1.40, 23.97)

4.64 (1.23, 21.95) 5.55 (1.63, 29.27)

3.92 (1.09, 23.24) 4.39 (1.12, 24.55)

V6

Male Female

6.41 (1.38, 23.65) 6.17 (1.61, 25.34)

6.42 (1.48, 21.18) 6.55 (1.71, 19.20)

6.68 (1.33, 22.47) 7.44 (1.83, 23.09)

5.93 (1.48, 21.11) 6.61 (1.83, 28.36)

4.88 (1.31, 21.40) 6.07 (1.27, 22.38)

wave in lead V1 was present in 47% of the women, but only in 12% of the men. Generally, the T-wave amplitude was higher in men than in women, especially in leads V2 –V4 , the highest T being in V3 in both sexes. Of the limb leads, lead II showed the tallest T waves in both sexes. T-wave amplitudes in men decreased with age, particularly in the precordial leads. In women, an age trend was less discernible.

3.6. R peak time R peak time (intrinsicoid deflection) was examined in view of the value ascribed to it in diagnosing ventricular hypertrophy and bundle branch block [10,18,19]. Normal values of the R peak time in V1 , V2 , V5 , and V6 are presented in Table 14. The upper limits in V1 and V2 vary considerably over the age groups. This is mainly caused by the presence of an R9 wave (which is considered a normal variant) in 3.4% (183 / 5360) of the subjects, resulting in longer

R peak times in some age groups. The upper limit of R peak time in lead V5 and V6 was |45 ms for women; values for men were slightly larger.

4. Discussion We determined normal ECG limits for a Chinese population, stratified according to age and sex. In the following, we discuss several established ECG criteria that may need adjustment when applied to a Chinese population. We also compare ECG differences between our Chinese population and other racial groups, although such a comparison has its difficulties. Not only do the available studies use different statistics to report normal limits, vary in their definition of age groups, and often report a limited set of parameters only, but they also differ in sample selection (random, population-based samples vs. samples of apparently healthy individuals). To our

J. Wu et al. / International Journal of Cardiology 87 (2003) 37–51

46

Table 11 J-point amplitude (mV): median (2nd percentile, 98th percentile) 18–29 Years

30–39 Years

Sex

I

Male Female

0.01 (20.05, 0.08) 0.00 (20.04, 0.05)

0.01 (20.04, 0.07) 0.00 (20.03, 0.05)

0.01 (20.04, 0.06) 0.00 (20.04, 0.05)

0.00 (20.05, 0.07) 0.00 (20.05, 0.06)

0.00 (20.04, 0.06) 0.00 (20.04, 0.06)

II

Male Female

0.03 (20.06, 0.14) 0.00 (20.07, 0.09)

0.03 (20.06, 0.13) 0.00 (20.06, 0.08)

0.02 (20.06, 0.12) 0.00 (20.07, 0.07)

0.02 (20.06, 0.11) 0.01 (20.07, 0.08)

0.01 (20.07, 0.10) 0.01 (20.08, 0.09)

III

Male Female

0.02 (20.09, 0.14) 0.00 (20.07, 0.08)

0.01 (20.07, 0.12) 20.01 (20.07, 0.08)

0.01 (20.07, 0.11) 0.00 (20.07, 0.08)

0.01 (20.08, 0.10) 0.01 (20.09, 0.09)

0.00 (20.08, 0.10) 0.01 (20.08, 0.08)

aVR

Male Female

20.02 (20.09, 0.04) 0.00 (20.05, 0.05)

20.02 (20.09, 0.04) 0.00 (20.05, 0.04)

20.01 (20.08, 0.04) 0.00 (20.05, 0.04)

20.01 (20.07, 0.04) 0.00 (20.06, 0.05)

0.00 (20.07, 0.05) 0.00 (20.05, 0.05)

aVL

Male Female

0.00 (20.08, 0.07) 0.00 (20.05, 0.06)

0.00 (20.07, 0.06) 0.01 (20.05, 0.05)

0.00 (20.07, 0.06) 0.01 (20.05, 0.05)

20.01 (20.07, 0.07) 0.00 (20.06, 0.06)

0.00 (20.06, 0.06) 20.01 (20.05, 0.06)

aVF

Male Female

0.02 (20.07, 0.15) 0.00 (20.07, 0.08)

0.02 (20.06, 0.13) 0.00 (20.06, 0.08)

0.02 (20.06, 0.11) 0.00 (20.07, 0.07)

0.01 (20.07, 0.10) 0.00 (20.07, 0.08)

0.01 (20.07, 0.10) 0.01 (20.07, 0.08)

V1

Male Female

0.04 (20.11, 0.16) 20.01 (20.11, 0.07)

0.04 (20.07, 0.16) 0.00 (20.07, 0.06)

0.03 (20.07, 0.15) 20.01 (20.08, 0.07)

0.03 (20.06, 0.14) 20.01 (20.11, 0.07)

0.02 (20.08, 0.13) 20.01 (20.08, 0.08)

V2

Male Female

0.15 (20.02, 0.36) 0.04 (20.08, 0.14)

0.13 (20.01, 0.30) 0.03 (20.07, 0.14)

0.11 (20.05, 0.27) 0.02 (20.06, 0.13)

0.09 (20.06, 0.25) 0.02 (20.09, 0.15)

0.07 (20.06, 0.22) 0.02 (20.09, 0.15)

V3

Male Female

0.12 (20.04, 0.34) 0.02 (20.08, 0.14)

0.11 (20.02, 0.29) 0.02 (20.07, 0.11)

0.08 (20.05, 0.26) 0.00 (20.07, 0.11)

0.06 (20.07, 0.22) 20.01 (20.09, 0.12)

0.04 (20.09, 0.19) 20.01 (20.12, 0.11)

V4

Male Female

0.06 (20.06, 0.24) 0.00 (20.09, 0.10)

0.05 (20.05, 0.19) 20.01 (20.08, 0.09)

0.03 (20.07, 0.18) 20.01 (20.08, 0.09)

0.01 (20.10, 0.17) 20.02 (20.13, 0.11)

20.01 (20.12, 0.12) 20.04 (20.13, 0.05)

V5

Male Female

0.02 (20.07, 0.15) 20.01 (20.10, 0.06)

0.02 (20.06, 0.13) 20.01 (20.06, 0.06)

0.01 (20.07, 0.13) 20.01 (20.08, 0.06)

0.00 (20.09, 0.10) 20.02 (20.11, 0.07)

20.02 (20.11, 0.08) 20.03 (20.12, 0.05)

V6

Male Female

0.01 (20.06, 0.12) 20.01 (20.07, 0.05)

0.01 (20.05, 0.11) 20.01 (20.06, 0.06)

0.01 (20.06, 0.10) 0.00 (20.06, 0.06)

0.00 (20.07, 0.08) 20.01 (20.08, 0.07)

20.01 (20.09, 0.08) 20.01 (20.10, 0.05)

knowledge, the only recent comprehensive report on normal limits based on an apparently healthy population is the study by Macfarlane and Lawrie [18] in white men and women. Therefore, we only make a limited comparison of racial ECG differences, and suggest that the paucity of data on normal limits in racial groups other than Caucasian warrants further investigation and documentation.

4.1. Heart rate Normal limits of sinus heart rate have mostly been set at 60 and 100 beats / min [20], although normal limits of 50 and 90 beats / min have also been suggested [21,22]. Our results show that the upper limit of normal heart rate for Chinese subjects is 95 beats / min. As to the lower limit, 15% (817 / 5360) of our subjects had a heart rate ,60 beats / min, with a prevalence of 18% in men and 9% in women. The

40–49 Years

50–59 Years

$60 Years

Lead

lower limit of heart rate in this study was close to 50 beats / min for men, not dependent on age, whereas women showed a decreasing trend with age from 57 to 51 beats / min. This suggests that traditional criteria of sinus tachycardia and especially bradycardia need adjustment when applied to a Chinese population.

4.2. P duration The upper limit of P-wave duration has traditionally been defined as 120 ms [18,22], a value based on single-lead measurement and allowing easy testing (120 ms equals 3 mm at standard 25 mm / s paper speed). Upper limits in this study range from 125 to 141 ms, with men consistently leaning towards slightly higher values than women, and increasing with age. These findings suggest that the established criterion for left atrial abnormality should be adjusted in Chinese subjects.

J. Wu et al. / International Journal of Cardiology 87 (2003) 37–51

47

Table 12 Positive T-wave amplitude (mV): median (2nd percentile, 98th percentile) Lead

Sex

18–29 Years

30–39 Years

40–49 Years

50–59 Years

$60 Years

I

Male Female

0.23 (0.10, 0.45) 0.19 (0.09, 0.35)

0.23 (0.08, 0.46) 0.18 (0.07, 0.34)

0.22 (0.08, 0.42) 0.20 (0.09, 0.36)

0.20 (0.06, 0.41) 0.19 (0.06, 0.34)

0.16 (0.05, 0.37) 0.17 (0.05, 0.36)

II

Male Female

0.36 (0.14, 0.63) 0.26 (0.10, 0.50)

0.33 (0.13, 0.57) 0.24 (0.08, 0.46)

0.29 (0.11, 0.54) 0.25 (0.09, 0.44)

0.26 (0.09, 0.47) 0.22 (0.07, 0.45)

0.26 (0.08, 0.48) 0.23 (0.07, 0.42)

III

Male Female

0.16 (0.04, 0.44) 0.10 (0.03, 0.28)

0.15 (0.03, 0.38) 0.10 (0.03, 0.24)

0.12 (0.03, 0.36) 0.09 (0.02, 0.25)

0.11 (0.03, 0.33) 0.08 (0.02, 0.25)

0.12 (0.03, 0.35) 0.10 (0.04, 0.29)

aVR

Male

–

–

–

Female

–

– n52

0.05 (0.03, 0.07) n53 0.03 (0.02, 0.06) n58

0.02 (0.02, 0.07) n516 0.03 (0.02, 0.10) n56

aVL

Male Female

0.10 (0.02, 0.28) 0.08 (0.03, 0.19)

0.11 (0.02, 0.30) 0.08 (0.02, 0.20)

0.10 (0.02, 0.26) 0.10 (0.03, 0.24)

0.09 (0.02, 0.28) 0.09 (0.03, 0.23)

0.08 (0.02, 0.23) 0.08 (0.02, 0.24)

aVF

Male Female

0.25 (0.06, 0.52) 0.17 (0.05, 0.37)

0.22 (0.06, 0.45) 0.16 (0.05, 0.34)

0.18 (0.05, 0.43) 0.15 (0.05, 0.33)

0.17 (0.05, 0.40) 0.14 (0.05, 0.35)

0.18 (0.05, 0.40) 0.16 (0.04, 0.35)

V1

Male Female

0.25 (0.05, 0.75) 0.08 (0.02, 0.28)

0.25 (0.04, 0.68) 0.09 (0.02, 0.32)

0.22 (0.04, 0.65) 0.07 (0.02, 0.30)

0.20 (0.04, 0.59) 0.08 (0.02, 0.26)

0.15 (0.03, 0.50) 0.08 (0.02, 0.30)

V2

Male Female

0.89 (0.34, 1.58) 0.39 (0.10, 0.84)

0.85 (0.32, 1.42) 0.39 (0.09, 0.79)

0.80 (0.27, 1.39) 0.35 (0.08, 0.77)

0.71 (0.22, 1.19) 0.34 (0.08, 0.85)

0.55 (0.14, 1.12) 0.32 (0.04, 0.72)

V3

Male Female

0.94 (0.43, 1.66) 0.48 (0.14, 0.94)

0.91 (0.34, 1.53) 0.49 (0.12, 0.91)

0.84 (0.28, 1.49) 0.43 (0.10, 0.88)

0.73 (0.24, 1.25) 0.39 (0.07, 0.96)

0.60 (0.16, 1.27) 0.35 (0.06, 0.82)

V4

Male Female

0.79 (0.32, 1.46) 0.44 (0.15, 0.80)

0.72 (0.24, 1.31) 0.44 (0.11, 0.84)

0.66 (0.19, 1.26) 0.39 (0.12, 0.83)

0.57 (0.15, 1.13) 0.35 (0.06, 0.84)

0.50 (0.12, 1.20) 0.31 (0.05, 0.74)

V5

Male Female

0.55 (0.22, 0.99) 0.37 (0.15, 0.64)

0.48 (0.17, 0.95) 0.35 (0.14, 0.65)

0.45 (0.13, 0.89) 0.33 (0.14, 0.66)

0.41 (0.09, 0.82) 0.31 (0.06, 0.67)

0.37 (0.08, 0.83) 0.28 (0.08, 0.61)

V6

Male Female

0.38 (0.16, 0.70) 0.28 (0.12, 0.51)

0.34 (0.13, 0.68) 0.26 (0.11, 0.50)

0.32 (0.11, 0.63) 0.27 (0.12, 0.50)

0.30 (0.09, 0.58) 0.25 (0.07, 0.50)

0.28 (0.07, 0.59) 0.24 (0.07, 0.45)

4.3. PR interval The median and upper limit of PR interval gradually increase with age, in particular in women. Generally, PR interval increases with decreasing heart rate. In our study, women show slower heart rates with increasing age, concomitant with progression of the PR interval. Upper normal limits of PR interval in this study were comparable to those in a Caucasian population [18]. When compared with an African population [23], median PR intervals in Chinese subjects were 10–15 ms shorter.

4.4. QRS duration The upper limit of normal QRS duration is usually set at 100 ms [22,24], although normal limits in excess of 110 ms have been reported in males [18].

In this study, 24.0% (1289 / 5360) of the individuals had a QRS duration greater than 100 ms. Instead, our results suggest a normal limit of QRS duration of 120 ms for Chinese men, and of 109 ms for women. Slightly lower values, but with similar sex differences, have been reported for a white population [18] and an African population [23]. Our results proved to be quite stable over the age groups, and imply that criteria involving QRS duration should be sex-specific when applied to a Chinese population.

4.5. QTc interval Although a number of other, and perhaps better, formulas than that of Bazett have been proposed, it remains the most widely applied clinical norm. The generally accepted upper normal limit of QTc interval is 440 ms [15]. In our data, the prevalence of QTc.

J. Wu et al. / International Journal of Cardiology 87 (2003) 37–51

48

Table 13 Negative T-wave amplitude (mV): median (2nd percentile, 98th percentile) Lead

Sex

18–29 Years

30–39 Years

40–49 Years

50–59 Years

$60 Years

I

Male

–

–

–

Female

–

– n52

0.03 (0.03, 0.04) n53 0.04 (0.02, 0.05) n55

0.05 (0.02, 0.19) n510 0.04 (0.02, 0.08) n55

0.05 (0.02, 0.08) n58 0.04 (0.02, 0.06) n512

0.04 (0.02, 0.07) n525 0.04 (0.02, 0.12) n56

II

Male Female

III

Male Female

aVR

Male Female

aVL

Male Female

aVF

Male Female

V1

Male Female

V2

– 0.03 (0.02, 0.04) n57

0.03 (0.02, 0.06) n510 0.03 (0.02, 0.14) n512

0.06 (0.02, 0.21) n5124 0.06 (0.02, 0.13) n599

0.06 (0.02, 0.23) n5219 0.05 (0.02, 0.14) n5128

0.06 (0.02, 0.21) n5274 0.05 (0.02, 0.21) n5196

0.06 (0.02, 0.25) n5197 0.06 (0.02, 0.21) n5101

0.06 (0.02, 0.16) n5189 0.05 (0.02, 0.18) n555

0.30 (0.14, 0.48) n5680 0.22 (0.10, 0.40) n5423

0.28 (0.13, 0.45) n5823 0.21 (0.09, 0.37) n5402

0.26 (0.11, 0.43) n5818 0.22 (0.11, 0.37) n5499

0.23 (0.09, 0.40) n5587 0.20 (0.07, 0.38) n5252

0.21 (0.07, 0.37) n5690 0.19 (0.07, 0.35) n5160

0.07 (0.02, 0.18) n5186 0.04 (0.02, 0.16) n530

0.05 (0.02, 0.15) n5202 0.04 (0.02, 0.14) n538

0.06 (0.02, 0.18) n5139 0.05 (0.02, 0.10) n526

0.06 (0.02, 0.17) n593 0.05 (0.03, 0.12) n524

0.06 (0.02, 0.18) n5156 0.05 (0.02, 0.12) n514

0.04 (0.02, 0.42) n59 0.03 (0.02, 0.11) n519

0.03 (0.02, 0.06) n513 0.03 (0.02, 0.09) n529

0.04 (0.02, 0.20) n531 0.04 (0.02, 0.11) n532

0.03 (0.02, 0.20) n532 0.04 (0.02, 0.09) n521

0.04 (0.02, 0.08) n544 0.03 (0.02, 0.06) n511

0.07 (0.02, 0.36) n571 0.09 (0.02, 0.22) n5209

0.06 (0.02, 0.25) n572 0.08 (0.02, 0.19) n5165

0.06 (0.02, 0.21) n586 0.08 (0.02, 0.21) n5243

0.06 (0.02, 0.22) n567 0.07 (0.02, 0.25) n5123

0.06 (0.02, 0.19) n5145 0.06 (0.02, 0.27) n577

n51 0.06 (0.04, 0.19) n57

0.04 (0.02, 0.08) n54 0.05 (0.03, 0.18) n510

0.11 (0.04, 0.16) n55 0.06 (0.02, 0.23) n512

n51 0.11 (0.02, 0.36) n54

0.06 (0.03, 0.11) n53 0.07 (0.02, 0.23) n57

0.16 (0.05, 0.29) n57 0.07 (0.02, 0.23) n57

n51 0.07 (0.03, 0.47) n56

0.09 (0.02, 0.19) n57 0.05 (0.02, 0.29) n510

0.15 (0.03, 0.65) n512 0.06 (0.02, 0.16) n58

n52 0.04 (0.02, 0.29) n57

0.08 (0.02, 0.27) n512 0.06 (0.03, 0.16) n57

0.08 (0.02, 0.51) n518 0.06 (0.02, 0.17) n58

n52 0.03 (0.02, 0.18) n57

0.06 (0.03, 0.22) n510 0.04 (0.02, 0.07) n510

0.05 (0.03, 0.29) n520 0.05 (0.02, 0.13) n512

Male Female

V3

n52 0.03 (0.02, 0.06) n56

– n52 0.10 (0.06, 0.16) n56

Male

0.04 (0.02, 0.16) n57 –

n51 Female V4

Male

n51

n51

–

–

Female V5

Male

n51

n51

–

–

Female

– n51

V6

Male Female

– n52 –

–

J. Wu et al. / International Journal of Cardiology 87 (2003) 37–51

49

Table 14 R peak time (ms): median (2nd percentile, 98th percentile) Lead

Sex

18–29 Years

30–39 Years

40–49 Years

50–59 Years

$60 Years

V1

Male Female

21 (12, 58) 20 (12, 28)

21 (13, 65) 20 (11, 30)

21 (12, 45) 20 (10, 30)

21 (12, 62) 20 (11, 45)

21 (11, 59) 20 (11, 57)

V2

Male Female

21 (10, 40) 20 (11, 43)

22 (13, 73) 20 (10, 39)

22 (11, 56) 22 (10, 37)

23 (12, 47) 22 (13, 39)

23 (12, 61) 22 (13, 71)

V5

Male Female

38 (28, 51) 34 (28, 44)

37 (28, 49) 35 (27, 45)

36 (28, 48) 36 (27, 45)

35 (26, 47) 34 (24, 46)

34 (26, 45) 32 (24, 43)

V6

Male Female

37 (28, 49) 35 (28, 43)

37 (29, 48) 35 (28, 44)

37 (28, 48) 36 (28, 45)

36 (27, 47) 35 (25, 47)

35 (26, 46) 33 (25, 43)

440 ms was 12.8% (223 / 1746) in women and 6.2% (223 / 3614) in men. Upper limits in both sexes tend to increase with age, and were always .440 ms. Also, women had consistently longer QTc intervals than men, up to 490 ms at an age $60. Thus, a uniform normal value of 440 ms regardless of sex and age does not seem appropriate in a Chinese population. It is noteworthy that our upper limits are 15–20 ms lower than those previously reported in a white population [18].

4.6. QRS axis In our data, we found a leftward shift of 258–308 with increasing age (Table 2). This age trend closely resembles previous findings in Caucasian, African, black Americans, and Hispanic populations [3,18,23]. Mean QRS axes for the various age groups (data not shown, mean values were 5–108 lower than the median values in Table 2) were similar to those reported for white populations [3,18]. Leftward shift of the frontal QRS axis with age has been associated with increasing obesity [3], resulting in an upward shift of the diaphragm and a more horizontal position of the heart.

4.7. QRS and T amplitudes Women tend to have smaller QRS complexes and lower T waves than men (Tables 8, 9 and 12). Causes of lower ECG amplitudes in women are thought to be a higher fat content [1], the influence of breast tissue [25], and smaller ventricular mass. Differences are most prominent in the younger age groups, possibly reflecting differences in level of physical activity between men and women [18, pp. 424–425].

R-wave amplitudes markedly increased with age in leads I and aVL, and decreased in II, III, and aVF, both for men and women (Table 8). These changes are concomitant with a frontal QRS axis shift to the left with age. Contrary to expectations, we found an increase of left-precordial R-wave amplitudes with increasing age in women. These results, however, corroborate those from the study of Chen et al. [6] who also found an increasing trend, although less marked than in our data. Interestingly, Rautaharju et al. [3] also reported an increase of RV5 amplitudes with age in normal-weight white and black women. Rotation of the QRS axis in the horizontal plane, obesity, and cardiac and chest changes with age are likely to affect the precordial amplitudes, but the interplay of these different factors is largely unknown. A longitudinal study in an apparently healthy population may further elucidate these issues. For all age groups, the Sokolow index was substantially higher for men than for women. Taking the Sokolow criterion (SV1 1RV5 .3.5 mV) [26] to represent left ventricular hypertrophy, we obtained a prevalence of 6.2% (224 / 3614) for men and 2.3% (40 / 1746) for women, with an overall prevalence of 4.9%. This demonstrates the specificity of the Sokolow criterion, especially for Chinese women. To reach the same specificity in men as in women, the threshold in men should be set at 4.2 mV. The mean values of the Sokolow index (data not shown, values |0.05 mV larger than corresponding median values) were consistently smaller (|0.2 mV) than those found by Macfarlane [18] in a Caucasian population, but comparable with those from a white population in a study by Rautaharju et al. [3]. In the latter study, Sokolow values for a black population

50

J. Wu et al. / International Journal of Cardiology 87 (2003) 37–51

were significantly higher, whereas those for a Hispanic population were lower. In our Chinese population, the Cornell criterion (RaVL1SV3 .2.0 mV in women and .2.8 mV in men) [27] proved to be highly specific, with a prevalence of only 1.2% (43 / 3614) for men and 0.9% (16 / 1746) for women. Our mean results (again |0.05 mV higher than the median values) were comparable with mean Cornell voltages in white women but lower than those in white men [3]; mean voltages in black Americans [3] and Africans [23] were (much) higher, although these differences should be interpreted with due caution because both these studies were based on non-selected populations.

4.8. R peak time WHO / ISCF recommendations define normal R peak time as #40 ms in lead V1 or V2 , and #50 ms in lead V5 or V6 [10]. In our data, the normal limit of R peak time in lead V5 and V6 was in reasonable agreement with these recommendations. However, the upper limit of normal in leads V1 and V2 was much larger than previously suggested [10], particularly in men, mainly caused by the presence of R9 waves. This suggests that R peak time in these leads is of limited value in diagnosing ventricular hypertrophy or bundle branch block. The size of our study population was over ten times the sample size in a previous study by Chen et al. [6] on normal limits for Chinese subjects, allowing much more precise percentile estimates. When we compare our findings with theirs, the trends and sex differences in our data are more marked and easier to interpret, particularly with respect to upper and lower limit estimates. For example, upper limits of P-wave duration in our study monotonically increase with increasing age, with consistently higher values for men than for women (Table 2). In Chen et al. [6], upper limits for men fluctuate around 132 ms, while they range from 112 to 146 ms for women. Many other such examples could be given. We believe our more stable results provide a firmer basis for comparison with and possibly adjustment of established ECG criteria. Summarizing, marked age and sex differences exist in the normal ECG limits of Chinese subjects. This

merits the definition of a set of age- and sex-specific ECG criteria for a Chinese population.

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J. Wu et al. / International Journal of Cardiology 87 (2003) 37–51 [21] Spodick DH, Raju R, Bishop RL, Rifkin RD. Operational definition of normal sinus heart rate. Am J Cardiol 1992;69:1245–6. [22] Chou TC. In: Electrocardiography in clinical practice, Philadelphia, PA: W.B. Saunders, 1996, pp. 321–39. [23] Zerkiebel N, Perret F, Bovet P et al. Electrocardiographic findings in a middle-aged African population in the Seychelles islands. J Electrocardiol 2000;33:1–15. [24] Fisch C. Electrocardiography. In: Braunwald E, editor, Heart disease: a textbook of cardiovascular medicine, Philadelphia, PA: W.B. Saunders, 1997, pp. 108–52.

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[25] LaMonte CS, Freiman AH. The electrocardiogram after mastectomy. Circulation 1965;32:746–54. [26] Sokolow M, Lyon TP. The ventricular complex in left ventricular hypertrophy as obtained by unipolar precordial and limb leads. Am Heart J 1949;37:161–86. [27] Casale PN, Devereux RB, Alonso DR, Campo E, Kligfield P. Improved sex-specific criteria of left ventricular hypertrophy for clinical and computer interpretation of electrocardiograms: validation with autopsy findings. Circulation 1987;75:565–72.